In early September 2022, in the no man’s land between the military frontlines of Ukraine and Russia, I had a decision to make: press on under fire, to establish a team of International Atomic Energy Agency safety experts at Europe’s largest nuclear power plant, or turn around. It had taken weeks of diplomacy to get this far; we decided to push on. Our armored vehicles zigzagged to avoid land mines, jostling the IAEA symbol on our jackets—a spinning atom surrounded by the two olive branches that the organization shares with the UN. As we drove past bombed buildings, burned-out cars, and families fleeing westward toward safer parts of Ukraine and its bordering countries, talk turned to whether Europe would have enough gas reserves for the winter.

The line between conflict and international consequences is thinning. Wars are displacing a record number of people and upending global trade and energy networks. The integrated global economy built after the Cold War, in which goods, capital, and technology flow relatively freely across borders, is fraying. The traditional separation of trade, security, development, and environmental concerns has become increasingly artificial. Cyber vulnerabilities, too, are expanding beyond mere technical concerns to affect vital infrastructure, energy grids, elections, and banking systems. As diplomatic standoffs and military conflicts disrupt supply chains, countries are moving to decouple.

The return of war to Europe has reshaped security perceptions and strategic calculations across the continent. In the Middle East, cycles of confrontation are generating consequences that extend well beyond the region, contributing to political divisions and disrupting energy markets, trade routes, food prices, and confidence in the world economy. In Asia, competition now spans military, economic, technological, and maritime domains. In Africa, demographic growth and economic potential run up against unequal access to finance and uneven institutional capacity. In Latin America and elsewhere, more sophisticated transnational criminal networks are exploiting global markets, financial systems, ports, logistics chains, and governance gaps. In this system, the consequences of failure travel faster and wider than ever before.

Meanwhile, multilateralism and international law and norms, which reduce the chances of catastrophic errors, provide stability, and offer shared solutions to shared problems, have come under strain as they struggle to adjust to these structural shifts. Most of the nuclear arms reduction and control treaties forged during the Cold War, such as the New Strategic Arms Reduction Treaty and the Intermediate-Range Nuclear Forces Treaty, are dead or weakened. Major nuclear arsenals are modernizing and expanding, rather than getting smaller, and the channels of communication that reduce the risk of miscalculation between powerful states have eroded. In some countries that have upheld their legal obligations to not develop nuclear weapons, debates have emerged over the merits of pursuing them.

Today, we are at greater risk of a major conflagration, including a nuclear one, than at any time since World War II. As the generations that experienced the horrors of two world wars and built the frameworks to prevent a third disappear, so........

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